1. Field of the Invention
The invention is directed to metal working operations and, more particularly, to an assembly for rotating a cutting insert about a central axis during a metal working operation. The subject invention is also directed to the cutting insert itself, the toolholder for cutting the insert, and a design to provide coolant to the cutting insert.
2. Description of Related Art
During a metal working operation, such as a turning operation, where a stationary insert is urged against a rotating workpiece, the insert cutting edge acting upon the workpiece is heated by the workpiece until the operation is complete or until the cutting edge begins to break down through a failure mechanism, such as creater wear or plastic deformation. To avoid these modes of failure, and to permit more efficient operation of the cutting insert, in the past, circular cutting inserts have been mounted upon toolholders, such that the cutting inserts were freely rotatable about the insert central axis. A particular cutting insert was then presented to the workpiece and oriented in such a fashion that the rotary motion of the workpiece on, for example, a lathe, imparted to the cutting insert a force acting in a direction tangential to the insert. The motion of the workpiece acted against the cutting insert not only to machine the workpiece but, furthermore, to rotate the circular cutting insert such that the cutting edge of the insert was continuously refreshed. As a result, under ideal conditions, no single segment of the cutting edge experienced prolonged exposure to the workpiece. Furthermore, the cutting edge operated at a lower temperature, thereby allowing greater cutting forces and improved efficiency of the metal working operation.
This type of spinning insert may exhibit extraordinarily long tool life and remarkable speeds. However, this same spinning insert may fail in an equally dramatic fashion when the cutting conditions change slightly, or when the cartridge bearings, used by the cutting insert for rotating, begin to deteriorate.
A method and assembly are needed capable of rotating the cutting insert about its own axis during a metal working operation, whereby the speed and direction of rotation is not determined by the rotation of the workpiece itself, but is determined by independent forces acting upon the cutting insert. In conjunction with this, a design is needed which may efficiently introduce coolant to the cutting insert.